1. Field of the Invention
The present invention relates to the art of manufacturing a sealed bearing rotary rock bit in general and, more particularly, to a method of determining the presence of water in the bearings and lubricant system of a sealed bearing rotary rock bit.
2. Description of the Prior Art
While drilling a borehole in search of oil or gas, extreme environmental conditions are encountered. The borehole may contain drilling mud which is used for carrying the rock cuttings out of the bottom of the borehole, as well as to provide cooling to some extent for the rock bit (as the bore hole depth increases, the temperature may increase as much as 2 degrees per hundred foot of depth so that temperatures of 300 to 350 degrees or higher are often encountered by the rock bit). The weight of the drill string is set on the rock bit to aid in penetrating the formations and may vary from 10,000 to 80,000 lbs. or higher. Rotary speeds of the rock bit may vary from 20 rpm to as high as 250 rpm; however, 50 to 70 rpm is most likely to be used.
During the assembly of a sealed bearing rotary rock bit, it is possible for water to enter the bearing and lubricant system on several occasions; for example:
An O-ring seal is assembled onto the arm and smear grease is placed on the bearing surfaces and the O-ring surfaces. The cone is then assembled onto the arm and ball bearings are inserted into the ball race through the ball plug hole. A ball plug is then inserted to retain the balls in the ball race. The ball plug is then welded and the arm and cone assembly submerged in water to cool the weld on the ball plug and arm. The weld is pressure tested under water.
Three arms and cone assemblies are assembled together and welded into a rock bit, after which the tool joint or pin area is heated to anneal the weld affected pin material before being threaded. During this time the lower section of the bit containing the bearings and seals is submerged in water to protect the seal and bearings from the heat. The tool joint is then threaded during which time a coolant at a high pressure is sprayed over the thread cutting tool and surface being threaded with much coolant spray impinging on other parts of the rock bit.
After threading the pin end of the bit, the nozzle bores leading from the central passageway are plugged using solid plugs with O-rings. The bit is then inverted and the threaded end pressed against a gasket using a pneumatic ram to force the gasket to seal the opening at the threaded end. An air line permits pressurizing the central passageway of the bit and the bit submerged in water to check for leaks along the weld which, if present, are repaired.
Thus, it is evident that the bit is time and again subjected to conditions that could introduce water into the lubricant system and bearings. A small amount of water present in the lubricant on the bearing surfaces will reduce the lubricating properties of the lubricant causing premature failure of the rock bit bearings. Heretofore, there was no step for detecting the presence of water in the bearing system and lubricant system during bit assembly.